Science

Mysterious Ailment Killing Manatees Off Florida Coast

By Pierre Dumont , Mar 19, 2013 11:59 AM EDT
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A record breaking number of manatees, over 180 in all, have died so far this year off the coast of southwest Florida.

A red tide has been blamed as the reason for the deaths. Red tides are caused by blooming of the algae "Karenia brevis" and get their name from the red-brown color they leave in the ocean. Neurotoxins created by the algae are deadly to fish, birds, sea turtles, marine mammals and possibly even humans, should they consume a sufficient amount of fish or breathe in enough of the toxins.

However, more dead manatees are appearing off the coast of east Florida, and scientists don't know why. Around 55 manatees have died in the Indian River Lagoon area and although the symptoms are similar to those of the manatees affected by the red tide, the scientists theorize that some other ailment is to blame.

"So far ... no sick manatees have been rescued, availing biologists with a live specimen to study for clues," says Craig Pittman of the "Tampa Bay Times," "They suspect the manatee deaths may be connected to back-to-back blooms of a [another species of] harmful algae, one that has stained the Indian River Lagoon a chocolate brown. Over the past two years the blooms wiped out some 31,000 acres of sea grass in the 156-mile-long lagoon that stretches along the state's Atlantic coast. Manatees eat sea grass, but with the sea grass gone, they may have turned to less healthful sources of nutrition."

There is a large difference between the cause of the algae blooms on the east coast and those on the west coast. Those in the eastern waters are caused by nutrient pollution from storm runoff. They are essentially a combination of manure, sewage, fertilizers and pet waste. This stands in contrast to the western red tide, which derives from a more varied source.

"In contrast to the many red tide species that are fueled by nutrient pollution associated with urban or agricultural runoff, there is no direct link between nutrient pollution and the frequency or severity of red tides caused by "K. brevis'," the Mote Marine Laboratory states. "Florida red tides develop 10-40 miles offshore, away from manmade nutrient sources. Red tides occurred in Florida long before human settlement, and severe red tides were observed in the mid-1900s before the state's coastlines were heavily developed. However, once red tides are transported inshore, they are capable of using manmade nutrients for their growth."

This makes the dead manatees off Florida's east coast somewhat of a mystery. Between 4,000 and 5,000 manatees, about half the world's population of the animal, exist off the coast of Florida. According to NOAA, large numbers of manatees died because of red tides near southwest Florida in 1963, 1982, 1996, 2002 and 2003, which seems to suggest that the rate of such incidents is increasing.

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